The present invention relates to a compact turbo-molecular pump, for evacuating a processing chamber used in a semiconductor device manufacturing process, having a high evacuation capability.
A conventional turbo-molecular pump is shown in FIG. 14. The pump is comprised of a pump casing 10 housing a rotor (rotation section) R and a stator (stationary section) S to form an axial exhaust vane section L1 and a screw groove exhaust section L3. The bottom section of the pump casing 10 is covered with a base section 14, which is provided with an exhaust port 14a. The top section of the pump casing 10 communicates the pump with an apparatus or conduit to be evacuated through an upper flange section 12a. The stator S is comprised primarily by a fixed cylindrical section 16 erected in the center of the base section 14, and the stationary sections of the axial exhaust vane section L1 and the screw groove exhaust section L3.
The rotor R comprises a main shaft 18 inserted inside the fixed cylindrical section 16 and a rotating cylinder section 20 attached thereto. The drive motor 22, an upper radial bearing 24, a lower radial bearing 26 and an axial bearing 28 are provided on the opposing surfaces of the main shaft 18 and the fixed cylindrical section 16. The axial bearing 28 comprises a target disk 28a provided at the bottom of the main shaft 18 and upper and lower electrical magnets 28b provided on the stator S. This structure permits the rotor R to be rotated at high speeds under five-axial active controls.
Axial exhaust vane section L1 includes an impeller comprising the rotary vanes 30 provided integrally with the upper outer periphery of the rotating cylinder section 20, and the stationary vanes 32 fixed on the interior of the casing 10 alternating with the rotary vanes 30, and produces evacuation action by the mutual interaction of the high-speed rotary vanes 30 and the stationary vanes 32.
A screw groove exhaust section L3 is provided at a downstream location of the axial exhaust vane section L1. In other words, the rotating cylinder section 20 has the screw groove section 54 having screw ridges 54a on its outer surface to surround the fixed cylindrical section 16, while, the stator S has a screw groove spacer 56 to surround the outer surface of the screw groove section 54. The screw groove exhaust section L3 performs its evacuation action by the drag effect of the screw ridges 54a of the screw groove section 54 rotating at high speed.
By providing the screw groove exhaust section L3 on a downstream side of the axial exhaust vane section L1, the turbo-molecular pump is able to handle a wide-range of flow rates. Although the illustrated example provided the screw grooves of the screw groove exhaust section L3 on the rotor side, the screw grooves may be provided on the stator side in some cases.
However, the volume of gas required by semiconductor processing apparatuses has been steadily increasing as a result of increasing wafer diameter, and consequently, the turbo-molecular pump has also been required to process an increasing volume of exhaust gas while maintaining the pressure inside the apparatus below a certain level and retaining a high compressive capability.
However, in the current technology, increase in the evacuation capacity is achieved through increasing the number of stages in the axial direction, causing the length and weight of the pump to increase. The result is not only a costly pump, but the valuable space inside a clean room begins to be occupied by the large pump apparatus. In addition, the safety of operation can be threatened if such a large rotor should fracture due to some difficulties because of the high dynamic torque being applied to the weighty pump.
It is an object of the present invention to provide a compact turbo-molecular pump that has a relatively short axial length and yet provides sufficient evacuation and compression capabilities.
The object has been achieved in a turbo-molecular pump comprising: a casing which contains an exhaust vane section having rotary vanes on a rotor section alternating with stationary vanes on a stator section, wherein the exhaust vane section comprises an axial exhaust vane section and a radial exhaust vane section disposed downstream of the axial exhaust vane section.
Accordingly, the overall performance of the present turbo-molecular pump is improved, because the present pump combines the axial exhaust vane section (exhibiting superior evacuation capability in the molecular flow region) with a radial exhaust vane section disposed in a downstream location operating at a higher pressure (exhibiting superior evacuation capability in a wide range of flow rates, from molecular flow to viscous flow regions). The radial exhaust vane section is, for example, made by placing the stationary vanes and rotary vanes in proximity and providing certain geometrical shaped ridges on the vanes so as to exhaust the gas in the radial directions by the effects produced by rotating vanes. A tortuous path in radial directions is thus created in multi-stages by having the rotary vanes alternating with the stationary vanes, and the pump performance (evacuation and compression characteristics) is improved without increasing the axial length of the pump. The surface irregularities such as ridges or grooves (protrusions or depressions) provided on the rotary vanes result in higher performance but they can be made much more readily on the stator side of the pump.
The radial exhaust vane section may comprise surface protrusions and depressions formed in a spiral shape on at least one of opposing surfaces of the stationary vanes or the rotary vanes. Impacting effect produced by such surface irregularities caused by rotation of the rotor section produces a superior evacuation efficiency. The radial exhausting structure is provided in the clearance space in the axial direction between the stationary vanes and the rotary vanes, therefore, compared with the screw type evacuation technique used in the conventional turbo-pump design, the pump performance is less sensitive to thermal or elastic deformation effects of the pump, and stable performance over a long service life of the pump is obtained.
In another aspect of the invention is a turbo-molecular pump comprising a casing which contains an exhaust vane section having rotary vanes on a rotor section alternating with stationary vanes on a stator section, wherein the exhaust vane section comprises a radial exhaust vane section, the radial exhaust vane section comprising surface irregularities formed in a spiral shape on at least one of opposing surfaces of the stationary vanes or the rotary vanes. The results of test by the inventors demonstrated that the gas evacuated toward the central region of the rotor section is able to overcome the centrifugal effects of the rotating vanes. Therefore, by having the rotary vanes alternating with the stationary vanes, a multi-stage tortuous path in the radial directions is created, and the pump performance is improved without increasing the axial length of the pump.
A screw groove exhaust section may be provided at an upstream location of the radial exhaust vane section for exhausting gases in an axial direction of the pump by means of screw grooves.
A screw groove exhaust section also may be provided at a downstream location of the radial exhaust vane section for exhausting gases in an axial direction of the pump by means of screw grooves.
The screw groove exhaust section may be provided between an inner surface of the rotor section and a fixed cylindrical section disposed on an inner side of the rotor section.
Stationary vanes and/or rotary vanes may be made of ceramics, titanium or titanium alloys. Such a pump would have improved strength, corrosion and thermal resistance.